Formula 1's sole tire suppliers Pirelli -- whose products came in for yet more criticism during Sunday's stop-start Spanish Grand Prix -- have admitted that some of the testing they conduct on their tires is "inadequate".

In 100 minutes of driving in Barcelona this weekend, a total of 82 pit stops were made by the field of 22 drivers -- prompting many involved at the top end of the sport to launch frustrated tirades about how intense tire degradation is ruining F1 racing.

Milan-based Pirelli have revealed they are announcing changes to their range of F1 tires on Tuesday, which may delight those who point out that many of F1's biggest stars sometimes lap slower than their counterparts in GP2.

"Winter tests are inadequate and carried out in conditions far from the reality of the season's races," Pirelli spokesman Francesco Tarallo told CNN.

"The cars are much faster this year than last year (as well)."

The admission of the inadequacy of the testing will increase the pressure on Pirelli, who were tasked in 2011 -- when they took on the sole supplier role -- with designing a less durable tire in order to force more pit stops and so create more unpredictable racing.

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Red Bull team boss Dietrich Mateschitz says this policy has gone too far, with the Austrian deeply critical of what he sees as the debilitating effects of fast-wearing tires after Sunday's fifth race of the season.

Ferrari's Fernando Alonso won on home soil, with Red Bull's Sebastian Vettel and Mark Webber finishing fourth and fifth respectively.

"Everyone knows what is happening," Mateschitz told Austrian reporters. "This has nothing to do with racing any more. This is a competition in tire management."

"Real car racing looks different. Under the given circumstances, we can neither get the best out of our car nor our drivers. There is no more real qualifying and fighting for the pole, as everyone is just saving tires for the race.

"If we would make the best of our car we would have to stop eight or 10 times a race, depending on the track."

Barcelona's Circuit de Catalunya is always tough on tires, but even Pirelli's motorsport director Paul Hembery felt that the level of pit stops -- with Alonso changing tires four times -- was too much.

"Strategy was again at the forefront of the Spanish Grand Prix, which as usual was very demanding on the tires because of the unique characteristics of this circuit," the Briton said.

"This is why we saw high levels of degradation, which should not be seen again to this extent for the rest of the year. Our aim is to have between two and three stops at every race, so it's clear that four is too many: in fact, it's only happened once before, in Turkey during our first year in the sport."

In that 2011 Turkish Grand Prix, Red Bull duo Vettel and Webber finished first and second respectively but the German, a three-time world champion, concedes that his team's driving is having a negative effect on the Pirellis.

"The first three cars were a little bit too fast for us and regarding looking after the tires, they did a better job," said Vettel, who leads the championship by four points from Lotus's Kimi Raikkonen (who finished second on Sunday).

"We need to catch up; we're not going the pace of the car, we're going the pace of the tires and obviously we do something to make the tires wear more."

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Tire degradation was the major talking point on Sunday, with Force India driver Paul Di Resta so bewildered by the number of stops that he radioed his team during the race to ask: "Can anybody tell me what is going on?"

Di Resta was the highest-placed Briton in the race, finishing seventh, just ahead of compatriot Jenson Button --- who shed further light on the effects of the tires in his post-race comments.

"When we're going round doing laps three seconds slower than a GP2 car did in qualifying, and only six seconds quicker than a GP3 car did in the race, there's something wrong," the McLaren driver said.

"This is the pinnacle of motor sport. We shouldn't be driving round so slowly to look after the tires."

Button added that even the thrill of overtaking has diminished considerably, since drivers know that they are often going past because "the other guy's tires are destroyed", while the need to ensure that the tires do not get too hot or cold demand extreme concentration from those at the wheel.

So drivers may be buoyed by the changes that Pirelli are set to announce on Tuesday.

"We'll be looking to make some changes, in time for Silverstone, to make sure that we maintain our target and solve any issues rapidly," said Hembery.

Before the British Grand Prix takes place on June 28-30, there are two more races where the drivers will have to use the existing tires.

The first takes place on May 26 in Monaco, where tire degradation is rarely an issue given the narrow streets and slow corners, whereas next month's Canadian GP may well throw up similar issues to the pain in Spain suffered by most drivers on Sunday.